Vibratory screeds are frequently employed to impart vibrations to poured concrete for tamping and leveling of the concrete as it is finished. The screed eliminates the tedious manual labor involved in finishing the concrete and thereby provides greater productivity as well as improving the quality of the finished concrete slab by providing more accurately controlled slab surfaces as well as controlling the crown.
U.S. Pat. No. 4,758,114 described a screed formed of a plurality of generally triangular frame members which are disposed at an acute angle, preferably about 45.degree., to the longitudinal axis of the screed. Screed plates are connected to the lower end of each triangular frame member, while the upper apex of each frame member is provided with a cradle that receives a ridge tube.
As disclosed in the aforementioned patent, vibration is imparted to the screed through a power source, such as a gasoline engine, which is mounted on the screed and the drive shaft is operably connected to a vibratory shaft which is journalled within hubs in the bases of the triangular frame members. As disclosed in the patent, the shaft is mounted eccentricly with respect to the hubs and the eccentric mounting provides vibratory motion for the screed.
In practice, the screed may have a substantial length, perhaps up to 50 or 60 feet, and may be composed of a number of screed sections which are connected together to provide the desired length for the concrete slab to be finished. The shaft of each screed section is connected to the shaft of adjacent screed sections by a flexible coupling arrangement. In this coupling construction, the end of each shaft is secured within an eccentric bore in a metal connecting member or sleeve, and a flexible splined tubular coupling connects adjacent sleeves together. More particularly, the outer surface of each sleeve is provided with external splines which mate with internal splines in the flexible coupling. With this construction, the spline connection transmits rotation between the shafts of the screed sections.
It is necessary that the eccentricity of the shafts be aligned, otherwise the harmonics will be upset and consistent vibrations will not be obtained throughout the length of the screed. If the eccentricity of the shafts is not in alignment, the vibrations will be either partially or fully cancelled and increased stress will be imparted to the shaft bearings and the structural components of the screed frame.
It has been found that it is extremely difficult in the field to properly align the eccentricity of the shafts. Attempts have been made to mark the sleeves to indicate the location of eccentricity and the workman in the field is then required to align the marks as the sleeves are inserted within the ends of the flexible coupling. This system has not proved satisfactory because the marks tend to become obliterated and workmen may not be fully apprised of the purpose of the marks with the result that the eccentricity of the shafts is not properly aligned and the vibrations are cancelled out and not maximized.